Generally, discharge lamps operable from 50 or 60 hertz alternating current voltage sources emit radiation in the visible region of the spectrum. These discharge lamps may be in the form of high intensity discharge metal vapor lamps such as mercury vapor, metal halide and high pressure sodium lamps for example. Normally, the discharge lamp has a negative volt-ampere characteristic and the current of such a plasma will tend to continually increase in magnitude if not restrained by a current limiter or ballast in series connection with the lamp.
Typically, metal vapor discharge lamps employed with a series connected inductive ballast are selected to have a voltage operational value substantially equal to about 50% of the rms value of a voltage source. Thus, a lamp operable from a 120-volt AC voltage source would have a design center voltage of about 52-volts and this voltage could rise as much as 25-volts over the life of the discharge lamp. However, this increase in operational voltage will undesirably reach a level whereat the voltage source no longer provides a potential sufficient to sustain operation of the lamp and the lamp is undesirably extinguished.
One known technique employed to increase this potential available to the discharge lamp is a step-up transformer and a fixed capacitor. In such apparatus, the source potential is stepped-up to a higher value whereby the level of potential whereat the lamp is extinguished is raised to a higher level than was previously available. Unfortunately, transformers are expensive, cumbersome and heavy which adds a multitude of undesirable features to the apparatus.
Another known apparatus for improving the operation of a ballast and discharge lamp is suggested in U.S. Pat. No. 3,996,495 issued to Herman on Dec. 7, 1976 and bearing the title "High Efficiency Ballast System For Electric Discharge Lamps". Therein, a non-linear capacitor is connected to a conventional high resistance transformer and allegedly improves a lamp current crest factor. Thus, lamp efficiency is reportedly improved because of an improved lamp current crest factor. In this manner, lamp current can be reduced without loss of light output. However, starting and maintaining ignition of increased wattage lamps remains a problem.
Another known apparatus suggesting improved starting and operating of fluorescent lamps is proposed in U.S. Pat. No. 4,079,292 issued to Kaneda on Mar. 14, 1978. Therein, an oscillation booster circuit is utilized to provide reignition energy to a discharge lamp in each half cycle of an AC power source. Thus, a relatively small inductor ballast may be utilized in conjunction with a relatively high voltage discharge lamp. However, auxiliary booster oscillator circuitry as well as the switching circuitry associated therewith are obvious disadvantages in so far as apparatus cost are concerned.
Additionally, United Kingdom Pat. No. 2,066,801 A published July 15, 1981 and issued to TDK Electronics Company, Ltd. suggests a non-linear dielectric element, the composition thereof, and a circuit utilizing the device with a lamp and a relatively complex preheating circuit for starting a lamp. Primarily, fabrication of this non-linear dielectric element is discussed and claimed.
Still another apparatus is suggested in an application bearing U.S. Ser. No. 639,608 entitled "Discharge Lamp Operating Apparatus And Method" filed Aug. 10, 1984 and assigned to the Assignee of the present application. Therein, a discharge lamp starting and operating apparatus includes a discharge lamp having an operating voltage not less than about 75% of the rms value of a voltage source. Therein, a fluorescent lamp shunted by a non-linear dielectric element and coupled by an inductive ballast to a pair of terminals connectable to the voltage source.